(a) Field of the Invention
The present invention relates to a mask for silicon crystallization, and a method for forming a polysilicon thin film using the same.
(b) Description of the Related Art
A silicon thin film that is deposited to form a thin film transistor (“TFT”), which may be used as a switching element in an active liquid crystal display or organic light emitting device, is formed by a plasma enhanced chemical vapor deposition (“PECVD”) process. Advantages to PECVD processing are that the resulting silicon layer has substantial uniformity and the deposition may be rapidly accomplished. Elements having high electron mobility are required for products such as a system on glass (“SOG”) in which an amorphous silicon layer is formed by PECVD and crystallized into polysilicon by a laser, and then a low temperature polycrystalline silicon (“LTPS”) for manufacturing a thin film transistor using the polysilicon.
However, the amorphous silicon layer formed through the PECVD includes a large amount of hydrogen due to SiH4 or Si2H6 used as a source gas and H2 as a carrier gas in the deposition process, and the large amount of hydrogen temporarily absorbs the laser having high energy under the laser crystallization such that it is vaporized and explosively out-gassed. Accordingly, the amorphous silicon is crystallized and simultaneously many voids are produced, such that a dehydrogenation process is inevitably required through heat treatment before crystallization to avoid the explosive out-gassing. Therefore, an additional apparatus is required and the process time is increased, such that they are many difficulties in the producing process of LTPS.